Methods of forming a polymeric material via self-assembly of amphiphilic material and related template structures

ABSTRACT

Methods for fabricating sub-lithographic, nanoscale microchannels utilizing an aqueous emulsion of an amphiphilic agent and a water-soluble, hydrogel-forming polymer, and films and devices formed from these methods are provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/473,748, filed May 17, 2012, pending, which is a divisional of U.S.patent application Ser. No. 11/726,674, filed Mar. 22, 2007, now U.S.Pat. No. 8,557,128, issued Oct. 15, 2013, the disclosure of each ofwhich applications and patents is hereby incorporated in its entiretyherein by this reference.

TECHNICAL FIELD

Embodiments of the invention relate to nanofabrication techniques and,more particularly, to methods for preparing nanoscale microstructuresand microchannels and to devices resulting from those methods.

BACKGROUND

As the development of nanoscale mechanical, electrical, chemical, andbiological devices and systems increases, new processes and materialsare needed to fabricate such devices and components. Opticallithographic processing methods are not able to accommodate fabricationof structures and features at the nanometer level. The use ofself-assembling diblock copolymers presents another route to patterningat nanometer dimensions. Diblock copolymer films spontaneously assembleinto periodic structures by microphase separation of the constituentpolymer blocks after annealing, for example, by thermal annealing abovethe glass transition temperature of the polymer or by solvent annealing,forming ordered domains at nanometer-scale dimensions. Following selfassembly, one block of the copolymer can be selectively removed and theremaining patterned film used as an etch mask for patterning nanosizedfeatures into an underlying substrate. Since the domain sizes andperiods (L_(o)) involved in this method are determined by the chainlength of a block copolymer (MW), resolution can exceed othertechniques, such as conventional photolithography, while the cost of thetechnique is far less than electron beam (e-beam) lithography or extremeultraviolet (EUV) photolithography, which have comparable resolution.

The film morphology, including the size and shape of themicrophase-separated domains, can be controlled by the molecular weightand volume fraction of the AB blocks of a diblock copolymer to producelamellar, cylindrical, or spherical morphologies, among others. Forexample, for volume fractions at ratios greater than about 80:20 of thetwo blocks (AB) of a diblock polymer, a block copolymer film willmicrophase separate and self-assemble into a periodic spherical domainswith spheres of polymer B surrounded by a matrix of polymer A. Forratios of the two blocks between about 60:40 and 80:20, the diblockcopolymer assembles into a periodic hexagonal close-packed or honeycombarray of cylinders of polymer B within a matrix of polymer A. For ratiosbetween about 50:50 and 60:40, lamellar domains or alternating stripesof the blocks are formed. Recently, graphoepitaxy, which involves theuse of lithographical-defined topographical features to direct blockcopolymer assembly, has been used in forming registered, self-assembleddiblock copolymer structures.

Although diblock copolymers are receiving attention for the ability toself-assemble and form sub-lithographic ordered features, there areinherent limitations in the use of these materials including anapproximate minimal feature size of 10 nm and relatively slow rates offormation of ordered structures on the order of hours.

It would be useful to provide a method of fabricating nanoscalemicrostructures and microchannels that overcome these problems.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described below with reference to thefollowing accompanying drawings, which are for illustrative purposesonly. Throughout the following views, the reference numerals will beused in the drawings, and the same reference numerals will be usedthroughout the several views and in the description to indicate same orlike parts.

FIG. 1 illustrates a diagrammatic top plan view of a portion of asubstrate at a preliminary processing stage according to someembodiments of the present disclosure, showing the substrate withtrenches. FIG. 1A is an elevational, cross-sectional view of thesubstrate depicted in FIG. 1 taken along line 1A-1A.

FIGS. 2-5 illustrate diagrammatic top plan views of a portion of asubstrate at various stages of processing according to an embodiment ofthe present disclosure to provide hydrophilic trench ends. FIGS. 2A-5Aand 2B-5B illustrate elevational, cross-sectional views of the substrateshown in FIGS. 2-5 taken along lines 2A-2A to 5A-5A and lines 2B-2B to5B-5B, respectively.

FIG. 6 illustrates an elevational, cross-sectional view of a portion ofthe substrate depicted in FIGS. 1 and 1A at a subsequent processing stepaccording to another embodiment of the disclosure to provide hydrophilictrench ends.

FIGS. 7 and 8 illustrate diagrammatic top plan views of the substrateshown in FIG. 6 in subsequent processing steps. FIGS. 7A and 8A areelevational, cross-sectional views of the substrate shown in FIGS. 7 and8 taken along lines 7A-7A and 8A-8A, respectively.

FIG. 9 is an elevational, cross-sectional view of the substrates shownin FIGS. 9A and 9B. FIGS. 9A and 9B (taken along lines 9A/9B-9A/9B ofFIG. 9) are diagrammatic top plan views of the substrates shown,respectively, in FIG. 5 and FIG. 1 at a subsequent processing step,according to different embodiments of the disclosure.

FIG. 10 illustrates an elevational, cross-sectional view of thesubstrate shown in FIG. 9A at a subsequent processing step.

FIGS. 11 and 12 are diagrammatic top plan views of the substrate of FIG.10 at subsequent processing stages. FIGS. 11A and 12A are elevational,cross-sectional views of the substrate shown in FIGS. 11 and 12 takenalong lines 11A-11A and 12A-12A, respectively.

FIG. 13 illustrates a diagrammatic top plan view of a portion of asubstrate at a preliminary processing stage according to anotherembodiment of the present disclosure. FIGS. 13A and 13B are elevational,cross-sectional views of the substrate depicted in FIG. 13 taken alonglines 13A-13A and 13B-13B, respectively.

FIG. 14 is a diagrammatic top plan view of the substrate shown in FIG.13 at a subsequent processing stage. FIGS. 14A and 14B are elevational,cross-sectional views of the substrate shown in FIG. 14, taken alonglines 14A-14A and 14B-14B, respectively. FIG. 14C is an elevational,cross-sectional view of the another embodiment of the substrate shown inFIG. 14, taken along line 14C-14C.

FIG. 15 illustrates an elevational, cross-sectional view of thesubstrate shown in FIG. 14A, at a subsequent processing step.

FIGS. 16 and 17 illustrate a diagrammatic top plan view of the substrateshown in FIG. 15 at a subsequent processing stages. FIGS. 16 and 17 and16B and 17B are elevational, cross-sectional views of the substrateshown in FIGS. 16 and 17 taken, respectively, along line 16-16A, line17A-17A, line 16B-16B, and line 17B-17B.

FIGS. 18A and 18B are elevational, cross-sectional views of thesubstrate shown in FIG. 17 taken, respectively, along line 18A-18A andline 18B-18B, at a subsequent processing stage.

FIG. 19 is an elevational, cross-sectional view of the substrate shownin FIG. 18A at a subsequent processing stage.

FIGS. 20-24 are elevational, cross-sectional views of the substrateshown in FIG. 5B at subsequent processing stages according to anotherembodiment of the present disclosure.

DETAILED DESCRIPTION

The following description with reference to the drawings providesillustrative examples of devices and methods according to embodiments ofthe invention. Such description is for illustrative purposes only andnot for purposes of limiting the same.

In the context of the current application, the term “semiconductorsubstrate” or “semiconductive substrate” or “semiconductive waferfragment” or “wafer fragment” or ^(“)wafer” will be understood to meanany construction comprising semiconductor material, including, but notlimited to, bulk semiconductive materials such as a semiconductor wafer(either alone or in assemblies comprising other materials thereon) andsemiconductive material layers (either alone or in assemblies comprisingother materials). The term “substrate” refers to any supportingstructure, including, but not limited to, the semiconductive substrates,wafer fragments, or wafers described above.

“L_(o)” is the inherent pitch (bulk period or repeat unit) of structuresthat self assemble upon annealing from a self-assembling (SA) blockcopolymer or a blend of a block copolymer with one or more of itsconstituent homopolymers.

“Hydrogels” are cross-linked soluble polymers that swell because of anaffinity for water but do not dissolve in water due to structural and/orchemical crosslinks.

The methods overcome limitations of fabricating films fromself-assembling block copolymers. In embodiments of the invention, themethods utilize a trench template defined either lithographically or byuse of a film template formed by the graphoepitaxial self-assembly of alamellar block copolymer inside a wider trench and selective removal ofone of the assembled blocks to form films that can be utilized, forexample, in etching sub-10 nm features in a substrate.

Steps in a method for fabricating nanoscale microstructures andmicrochannels according to an embodiment of the invention areillustrated in FIGS. 1-12.

Referring to FIGS. 1 and 1A, a substrate 10 with an overlying materiallayer 12 is shown. In the described embodiment, the material layer 12 ispatterned to form trenches 14. The trenches 14 can be formed using alithographic technique such as photolithography, extreme ultraviolet(EUV) lithography, proximity X-rays, electron beam (e-beam) lithography,as known and used in the art. Conventional photolithography can providetrenches 14 with widths down to about 60 nm. E-beam and EUV lithographycan produce smaller features, although at a slower rate and higherexpense.

A method called “pitch doubling” or “pitch multiplication” can also beused for extending the capabilities of photolithographic techniquesbeyond their minimum pitch, as described, for example, in U.S. Pat. No.5,328,810 (Lowrey et al.), U.S. Patent Publication No. 2006/0281266(Wells), and U.S. Patent Publication No. 2007/0023805 (Wells et al.),the disclosures of which are incorporated by reference herein. Briefly,a pattern of lines is photolithographically formed in a photoresistlayer overlying a layer of an expendable material, which in turnoverlies a substrate. The expendable material layer is etched to formplaceholders or mandrels. The photoresist is stripped. Spacers areformed on the sides of the mandrels, and the mandrels are then removed,leaving behind the spacers as a mask for patterning the substrate. Thus,where the initial photolithography formed a pattern defining one featureand one space, the same width now defines two features and two spaces,with the spaces defined by the spacers. As a result, the smallestfeature size possible with a photolithographic technique is effectivelydecreased down to about 30 nm or more.

In some embodiments, trenches or grooves with widths in the about 10 nmto 30 nm range can be defined using techniques involving graphoepitaxialself-assembly of lamellar-phase block copolymers to provide an etch maskfor patterning underlying substrate stacks, e.g., silicon over siliconoxide, as described with reference to FIGS. 13-19.

As illustrated in FIGS. 1 and 1A, each trench 14 is structured withopposing sidewalls 16, opposing ends 18 (which may also be referred toherein as edges), a floor 20 (which may also be referred to herein as abottom surface), a width (w_(t)), a length (l_(t)), and a depth (D_(t)).In some embodiments, the trench dimension is about 20-200 nm wide(l_(t)) and about 1600-2400 nm in length (l_(t)), with a depth (D_(t))of about 50-500 nm. Substrate 10 is exposed as the floor 20 of thetrench 14, and a portion of the material layer 12 forms a spacerinterval or crest 12 a between the trenches 14. The trenches 14 arestructured such that the sidewalls 16 are hydrophobic and preferentialwetting to the surfactant component of the described polymer/surfactantemulsion, and the floor 20 of the trench 14 is hydrophilic such that thepolymer component will assemble within the center of the trench 14.

In some embodiments, the substrate 10 is composed of an oxide layer(e.g., silicon oxide, SiO_(x), and the material layer 12 is a siliconlayer (with native oxide). Hydrophobic trench sidewalls 16 and ends 18can be provided by removing the native oxide from the surface of asilicon material layer 12 within the trenches 14 to formhydrogen-terminated silicon. H-terminated silicon can be prepared by aconventional process, for example, by a fluoride ion etch of silicon(with native oxide present), for example, by immersion in an aqueoussolution of hydrogen fluoride (HF) or buffered HF and/or ammoniumfluoride (NH₄F), by HF vapor treatment, by exposure to hot H₂ vapor, orby a hydrogen plasma treatment (e.g., atomic hydrogen).

In other embodiments, including embodiments in which the surfactantmaterial layer (e.g., surfactant monolayer 24) (FIGS. 9-11A) is removedby a wet extraction process (FIGS. 12 and 12A), the material layer 12can be composed of a carbonaceous film such as amorphous carbon, whichis semi-graphitic but not crystalline in nature, to provide hydrophobictrench sidewalls 16 and ends 18. In some embodiments, the amorphouscarbon can be a form of transparent carbon that is highly transparent tolight. Deposition techniques for forming a highly transparent carbon canbe found in A. Helmbold & D. Meissner, Optical Absorption of AmorphousHydrogenated Carbon Thin Films, 283(1-2) THIN SOLID FILMS 196-203(1996), the disclosure of which is incorporated herein by reference. Inaddition, amorphous carbon layers can be formed by chemical vapordeposition using a hydrocarbon compound, or mixtures of such compounds,as carbon precursors such as ethylene, propylene, toluene, propyne,propane, butane, butylene, butadiene, and acetylene. A suitable methodfor forming amorphous carbon layers is described in U.S. Pat. No.6,573,030 (Fairbairn et al.), the entire disclosure of which isincorporated herein by reference.

The trench floors 20 (e.g., of silicon oxide, which is inherentlyhydrophilic) can then be treated to provide a selectively graftablesurface. In some embodiments, a ligand (anchor, linker) having areactive moiety (e.g., an end group) can be grafted onto the surface ofthe oxide layer of the substrate 10 (with the reactive moiety orientedtoward the center of the trench 14). For example, in embodiments using aClick-based chemistry reaction for the formation of a hydrogel composedof PEO or PEG, an example of a useful linker or ligand is poly(ethyleneglycol) (PEG) functionalized with an alkyne group, as described, forexample, in Michael Malkoch et al., Synthesis of Well-Defined HydrogelNetworks Using Click Chemistry, CHEM. COMMC'NS 2774-76 (2006), thedisclosure of which is incorporated herein by reference. As described inMalkoch et al., PEG can be reacted with excess anhydride (e.g.,4-pentynoic anhydride) to derivatize both ends of the PEG moiety withalkyne groups. To provide a derivatized PEG ligand having a reactive endgroup that can be grafted onto the surface of an oxide layer, PEG can bereacted with an anhydride in an about 1:1 ratio to derivatize one end ofthe PEG moiety with an alkyne group and the other end with a hydroxylgroup. The mono-hydroxylated PEG ligands can then be grafted to an oxide(e.g., SiO₂) surface by spin-coating (e.g., from a 1% w/v solution intoluene) and heating to allow the terminal OH groups to diffuse to andreact with the oxide layer, as described, for example, in P. Mansky etal., Controlling Polymer-Surface Interactions with Random CopolymerBrushes, 275 (5305) SCIENCE 1458-60 (1997), the disclosure of which isincorporated by reference herein. The PEG group of the attached ligandprovides a linker to the PEG or PEO moieties from the hydrogel emulsion.Non-grafted material can be removed by rinsing with an appropriatesolvent (e.g., toluene).

In another embodiment, an alkyne-functionalized PEG ligand containing asilane group such as trichlorosilane or trialkoxysilane can be graftedto an oxide surface. For example, a mono-hydroxylated PEG ligand can bereacted with tetrachlorosilane (SiCl₄) or tetraethoxysilane Si(OC₂H₅)₄to produce the desired compound, which can be applied to the trenchfloors 20, for example, by spin-on application. Conditions for theapplication of trialkoxy and trichlorosilane compounds are described,for example, by Barry Arkles, Silane Coupling Agents: Connecting AcrossBoundaries (v2.0), Gelest, Inc., Morrisville, Pa. (2006), the disclosureof which is incorporated herein.

In other embodiments using a free radical polymerization process for thepreparation of the hydrogel, an example of a suitable linker is PEGpolymer functionalized with an acrylate group at one end such as a PEGacrylate, or PEG methacrylate, which can be obtained from a commercialsource such as Sigma-Aldrich Co. (St. Louis, Mo.).

In other embodiments, the surface of both the trench floor 20 and thetrench ends 18 can be treated to be hydrophilic such that aqueous phaseof the emulsion wets both the trench floor 20 and ends 18, and thesurfactant layer (e.g., surfactant monolayer 24 (FIGS. 9-11A)) formssolely along the hydrophobic trench sidewalls 16, as in FIGS. 9 and 9A.In some embodiments, the material layer 12 can be structured to providea silicon surface exposed at the sidewalls 16 that is treated to removenative oxide to form H-terminated silicon and to provide an oxidesurface exposed at the ends (edges) 18 (and floor 20) of the trenches 14that is treated with a PEG ligand.

For example, referring to FIGS. 2-2B, a material layer 12 of silicon canbe deposited and etched lithographically to form trenches 11 that exposean underlying SiO_(x) layer of the substrate 10. Then, as illustrated inFIGS. 3-3B, a SiO_(x) layer 13 can be deposited to overfill the trenches11 and removed, for example by chemical-mechanical planarization (CMP),to expose the surface of the silicon material layer 12 and SiO_(x) layer13 within the trenches 11, as shown in FIGS. 4-4B. As depicted in FIGS.5-5B, the silicon material layer 12 can then be etched lithographicallyusing a photoresist mask to define the trenches 14 with the SiO_(x)layer of the substrate 10 exposed as the trench floor 20, the SiO_(x)layer 13 as the trench ends 18, and the silicon material layer 12exposed as the sidewalls 16.

In another embodiment, a silicon layer 12′ can be deposited and etchedlithographically to form trenches 14′ that expose an underlying SiO_(x)layer 10′ (as trenches 14 expose the substrate 10 in FIGS. 1 and 1A).Then, as illustrated in FIG. 6, a SiO_(x) layer 13′ can be deposited tooverfill the trenches 14′ and removed, for example, bychemical-mechanical planarization (CMP), to expose the surface of thesilicon layer 12′ and SiO_(x) layer 13′ within the trenches 14′, asshown in FIGS. 7 and 7A. As depicted in FIGS. 8 and 8A, portions of theSiO_(x) layer 13′ can then be etched lithographically using aphotoresist mask to redefine the trenches 14′ with the SiO_(x) layer 10′exposed as the trench floor 20′, the SiO_(x) layer 13′ as the trenchends 18′, and the silicon layer 12′ exposed as the sidewalls 16′.

In either of the embodiments depicted in FIGS. 5-5B or FIGS. 8 and 8A,an aqueous fluoride treatment can be briefly conducted to remove nativeoxide on the material layer 12 (FIGS. 5-5B) or silicon layer 12′ (FIGS.8 and 8A) (to form H-terminated silicon sidewalls 16, 16′) whileminimizing etching of the SiO_(x) layers (i.e., SiO_(x) layer ofsubstrate 10, SiO_(x) layer 10′, and SiO_(x) layer 13, 13′). A PEGcoupling agent can then be applied and bound to hydroxyl (−OH) groups onthe SiO_(x) floor 20, 20′ and ends 18, 18′ of the trenches 14, 14′ in aninert atmosphere (e.g., nitrogen, argon, etc.) to minimize thereformation of native oxide on the silicon sidewalls 16, 16′.

Referring now to FIG. 9, an aqueous emulsion layer 22 composed of anamphiphilic agent (e.g., surfactant) and a water-soluble,hydrogel-forming polymer, with optional additives, is applied to fillthe trenches 14 and over the material layer 12 (and SiO_(x) layer 13).The polymer/surfactant emulsion (of the aqueous emulsion layer 22) canbe applied, for example, by casting, dip coating, spray coating,knife-edge coating, spin casting (spin-coating), and the like, such thatthe aqueous emulsion layer 22 is maintained in a liquid consistency toallow the hydrogel to set up and the surfactant monolayer 24 to form atthe trench sidewalls 16. Application of the emulsion can be conducted atabout room temperature (e.g., about 20-25° C.) to up to about 95° C.

Upon application of the emulsion, the surfactant component willself-assemble to form a surfactant monolayer 24 (SAM) along thehydrophobic trench surfaces, with a thickness of about 10 nm or less,typically about 3-10 nm, or about 3 nm. The establishment of thesurfactant monolayer 24 at the hydrophobic trench sidewalls 16 isdependent, at least in part, on the presence of water. The aqueous phase26 of the emulsion comprising the polymer component orients to thehydrophilic floors 20 at the center of the trenches 14. The rate ofself-assembly of the surfactant monolayer 24 (SAM) is relatively rapidat about 0.1-1 minute (or less), and is generally limited by the rate ofdiffusion of the surfactant to the hydrophobic surfaces (e.g., sidewalls16).

As illustrated in FIG. 9A, in embodiments in which the sidewalls 16 arehydrophobic (e.g., H-terminated silicon) and the trench floor 20 andends 18 are hydrophilic, the formation of the surfactant monolayer 24will occur solely along the trench sidewalls 16 with the polymer aqueousphase 26 of the emulsion wetting the trench floor 20 and ends 18. Inother embodiments in which both the trench sidewalls 16 and ends 18 arehydrophobic, the surfactant component of the emulsion will form asurfactant monolayer 24 on both the trench ends 18 and sidewalls 16, asshown in FIG. 9B.

Suitable water-soluble and hydrogel-forming polymers include, forexample, poly(ethylene oxide) (PEO) and poly(ethylene glycol) (PEG). Anexample of a PEG-based hydrogel material is described in Michael Malkochet al., Synthesis of Well-Defined Hydrogel Networks Using ClickChemistry, CHEM. COMMC'NS 2774-76 (2006), the disclosure of which isincorporated by reference herein. Briefly, a PEG-based hydrogel materialcan be prepared using Click chemistry, e.g., a copper-catalyzedcycloaddition with azide/acetylene coupling reactions, by reactingdiacetylene-functionalized and tetraazide-functionalized PEG derivativesat room temperature under aqueous conditions in the presence of coppersulfate (CuSO₄) and sodium ascorbate as a reducing agent; wherein ahydrogel can form in less than about 30 minutes at about roomtemperature.

In other embodiments, the hydrogel can be synthesized by thephotopolymerization of water-soluble vinyl monomers using visible or UVirradiation to form water-soluble polymers with two or more reactivegroups, as described, for example, by Kytai Truong Nguyen & Jennifer L.West, Photopolymerizable Hydrogels for Tissue Engineering Applications,23 (22) BIOMATERIALS 4307-14 (2002), the disclosure of which isincorporated by reference herein. Examples of photopolymerizablemacromers include the following: PEG acrylate derivatives (e.g.,Amarpreet S. Sawhney et al., Bioerodible Hydrogels Based onPhotopolymerized Poly(ethylene glycol)-co-poly(α-hydroxy acid)Diacrylate Macromers, 26 (4) MACROMOLECULES 581-87 (1993)); PEGmethacrylate derivatives (e.g., Elisseeff J et al., Photoencapsulationof Chondrocytes in Poly(ethylene oxide)-Based Semi-interpenetratingNetworks, 51 (2) J. BIOMEDICAL MATERIALS RESEARCH 164-71 (2000); Kim I Set al., Self-Assembled Hydrogel Nanoparticles Composed of Dextran andPoly(ethylene glycol) Macromer, 205 (1-2) INT'L J. PHARM. 109-16(2000)); polyvinyl alcohol (PVA) derivatives (e.g., U.S. Pat. No.5,849,810 (Müller) (entitled Photocrosslinked Polymers); P. Martens andK. S. Anseth, Characterization of Hydrogels Formed from AcrylateModified Poly(vinyl alcohol) Macromers, 41 (21) POLYMER 7715-22 (2000));and modified polysaccharides, such as hyaluronic acid derivatives (e.g.,Matsuda T et al., Photoinduced Prevention of Tissue Adhesion, 38 (3)ASAIO J. M154-57 (1992); Paul Bulpitt & Daniel Aeschlimann, New Strategyfor Chemical Modification of Hyaluronic Acid: Preparation ofFunctionalized Derivatives and Their Use in the Formation of NovelBiocompatible Hydrogels, 47 (2) J. BIOMEDICAL MATERIALS RESEARCH 152-69(hyaluronic acid-based hydrogels)); and dextran methacrylate (e.g., KimS H & Chu C C, Synthesis and Characterization of Dextran-methacrylateHydrogels and Structural Study by SEM, 49 (4) J. BIOMEDICAL MATERIALSRESEARCH 517-27 (2000), and Kim S H & Chu C C, In Vitro Release Behaviorof Dextrano-methacrylate Hydrogels Using Doxorubicin and Other ModelCompounds, 15 (1) J. BIOMATERIALS APPLICATIONS 23-46 (2000)(dextran-methacrylate hydrogel)); the disclosures of each of which areincorporated by reference herein.

In other embodiments, the hydrogel can be synthesized by the freeradical-induced crosslinking of PEG-diacrylates or PVA-diacrylates, asdescribed, for example, by P. Martens and K. S. Anseth, Characterizationof Hydrogels Formed from Acrylate Modified Poly(vinyl alcohol)Macromers, 41 (21) POLYMER 7715-22 (2000) (acrylate-modified poly(vinylalcohol) hydrogels); Sheng Lin-Gibson et al., Structure-PropertyRelationships of Photopolymerizable Poly(ethylene glycol) DimethacrylateHydrogels, 38 MACROMOLECULES 2897-902 (2005) (photopolymerizable PEGdimethacrylate hydrogels); Kai Guo & C. C. Chu, Synthesis andCharacterization of Novel Biodegradable Unsaturated Polyesteramide)/Poly(ethylene glycol) Diacrylate Hydrogels, 43 (17) J. POLYMERSCI. PART A: POLYMER CHEMISTRY 3932-44 (2005) (biodegradable unsaturatedpoly(ester-amide)s/PEG diacrylate hydrogels); and Chakravarthy S.Gudipati et al., Hyperbranched Fluoropolymer and Linear Poly(ethyleneglycol) Based Amphiphilic Crosslinked Networks as Efficient AntifoulingCoatings: An Insight into the Surface Compositions, Topographies, andMorphologies, 42 (24) J. POLYMER SCI. PART A: POLYMER CHEMISTRY 6193-208(2004) (hyperbranched fluoropolymer and linear PEG-based amphiphiliccrosslinked networks), the disclosures of each of which are incorporatedby reference herein.

In yet other embodiments, the hydrogel can be synthesized bycrosslinking cysteine-based peptides with vinyl sulfone-functionalizedmulti-armed PEG macromers, as described, for example, by M. P. Lutolf etal., Cell-Responsive Synthetic Hydrogels, 15 (11) ADVANCED MATERIALS888-92 (2003) (cell-responsive synthetic hydrogels), the disclosure ofwhich is incorporated by reference herein. In other embodiments, thehydrogel can be synthesized from PEG macromers and dendritic peptidecrosslinkers, as described, for example, by Michel Wathier et al.,Dendritic Macromers as In Situ Polymerizing Biomaterials for SecurityCataract Incisions, 126 (40) J. AM. CHEM. SOC'Y 12744-45 (2004) (peptidedendron with terminal cysteine residues mixed with PEG dialdehyde), thedisclosure of which is incorporated by reference herein.

The polymer is combined with an amphiphilic surfactant (exhibits bothhydrophilic and lipophilic (hydrophobic) characteristics) that will forma self-assembled monolayer (SAM) on the hydrophobic surfaces of thetrench. Suitable amphiphilic surfactants include, for example,phospholipids (anionic surfactants), such as phosphatidylcholines (PCs),phosphatidylserines (PSs), phosphatidylethanolamines,phosphatidylinositols, phosphatidylglycerols, phosphatidic acids,lysophospholipids, among others. Examples of suitablephosphatidylcholines (PCs) include dipalmitoyl-PC (DPPC),1-palmitoyl-2-oleoyl-PC (POPC), dioleoyl-PC (DOPC), and dilinoleoyl-PC(DLiPC), among others. Other useful surfactants include nonionicsurfactants, such as octylphenol ethoxylates, for example, TRITON™-XSeries surfactants, such as TRITON™ X-100 (C₁₄H₂₂O (C₂H₄O)_(n) where n=9to 10)), among others.

The surfactant is included in the emulsion at a concentration effectiveto form a surfactant monolayer 24 having a thickness of about 10 nm orless or about 3-10 nm. A suitable emulsion can be formulated with anabout 5-15% w/w of the polymer and an about 0.5-5% w/w of thesurfactant, based on the total weight of the emulsion.

Optionally, the emulsion can include a crosslinking adjuvant orcatalyst/cocatalyst. For example, in the use of Click chemistry tosynthesize a PEG-based hydrogel material, the emulsion can includecopper sulfate (e.g., at about 1% w/w) and sodium ascorbate, whereby theemulsion would be directly or about immediately dispensed. In the use offree radical cross-linking chemistry to synthesize the hydrogelmaterial, an appropriate peroxide or photoinitiator can be included, andthe emulsion layer can be crosslinked by exposure to UV light, focusede-beam, heat, etc., as appropriate to crosslink the polymer to form ahydrogel.

As a further option, the emulsion can include a compatible organicsolvent to modify the thickness of the surfactant layer over a range ofabout 3 nm to up to about 10 nm. Suitable solvents include, for example,C₈-C₂₄ alkanes (e.g., octane, nonane, decane, undecane, dodecane, etc.),cycloalkanes (e.g., cyclopentane, cyclohexane, etc.), and aromatichydrocarbons (e.g., benzene, toluene, etc.).

In addition, the emulsion can optionally include one or more hardeningagents to fill or strengthen the hydrogel. Suitable hardening agentsinclude, for example, inorganic nanoparticles, such as silicon dioxide(SiO₂); metal oxides, such as zirconium oxide (ZrO₂), titanium dioxide(TiO₂), cerium dioxide (CeO₂), aluminum oxide, Al₂O₃), iron oxide,vanadia, and tin oxide; carbonates, such as calcium carbonate; andcarbon black. Solvated metals that can be precipitated can also be usedas hardening agents. For example, in the use of Click chemistry tosynthesize the hydrogel, the inclusion of a copper catalyst at about 1%w/w that precipitates after formation of the hydrogel can providestrengthening of the gel. Other examples of solvated metals that can beused as hardening agents are described, for example, in Joseph Mindeland Cecil V. King, A Study of Bredig Platinum Sols, 65 (11) J. AM. CHEM.SOC'Y 2112-15 (1943) (using electrochemical reduction of metals underwater to produce sols of Pb, Sn, Au, Pt, Bi, Sb, As, Tl, Ag, and Hg),the disclosure of which is incorporated by reference herein.

An embodiment of a suitable emulsion composition can be formulated with:

about 5-15% w/w water-soluble, hydrogel-forming polymer;

about 1-5% w/w amphiphilic surfactant;

about 0-5% w/w organic solvent;

about 0-20% w/w (or more) hardening agent;

about 0-5% w/w cross-linking adjuvants; and

about 94-55% w/w water.

In some embodiments, after formation of the hydrogel with the aqueousphase 26 within the trenches 14, a liquid filler material can be appliedto the surfactant monolayer 24 and hydrogel of the aqueous phase 26 toreduce the impact of drying on the shape and adherence of the surfactantmonolayer 24 to the hydrophobic trench surfaces and to furtherstrengthen and reduce the porosity of the polymer hydrogel such that theshape of the hydrogel is retained after removal of the surfactantmonolayer 24 and it functions as an adequate mask during a plasmaetching process (see FIG. 12A, element 28 (a robust hydrogel 28)).

For example, in addition to the incorporation of inorganic nanoparticlesas hardening agents, a silicon ester, such as tetraethoxysilane ortetraethyl orthosilicate (TEOS, Si(OC₂H₅)₄) (either neat or as solutionin organic solvent or water), can be applied and allowed to diffuse intothe hydrogel of the aqueous phase 26 to form a silicon oxide gel viaconventional sol-gel reaction to fill in the shape of the hydrogel withan inelastic material. The diffusion process can be expedited byformulating an aqueous solution having either an acidic or basic pH. Inembodiments in which the hydrogel includes an oxide hardening agent(e.g., SiO₂, TiO₂, etc.), the resulting sol (e.g., silica sol) acts tofuse or precipitate the separate particles of the hardening agent into acontiguous mass or suspension within the hydrogel to further harden thehydrogel, which can remain partially porous.

In other embodiments, the surfactant monolayer 24 can be formed asdescribed in U.S. Pat. No. 6,884,842 (Soane et al.), the entiredisclosure of which is incorporated by reference herein. Briefly,surfactant monomers containing olefinic group(s), with surfacefunctional head groups that are complementary to a substrate surface,are applied to and self-assemble at a micelle-like interface on thesubstrate. The positions of the functional groups on the substrate arethen stabilized by crosslinking reactive groups on the monomers by afree radical polymerization method to form a thin, insoluble polymernetwork or mat. The resulting surfactant monolayer 24 has high thermaland solvent stability, is robust against the removal of water, and isnot disrupted by organic solvents such as alcohols that are releasedduring formation of a sol. The monomers for forming the surfactantmonolayer 24 are structured with a head group (e.g., alcohols,carboxylic acids, amides, amines, phosphates, sugars, disaccharides,etc.), a crosslinking group (e.g., a free radically polymerizablemoiety, such as acrylates, methacrylates, acrylamides, vinyl ethers,epoxides, etc.), and a tail group fabricated and designed to havesurfactant functionality. Examples of compounds include acryloylatedsulfosuccinic acid ester surfactants, such as(bis(11-acryloylundecyl)sulfosuccinate),(bis-(3-acryloyl-2-ethylhexyl)sulfosuccinate), and(bis-2-acryloyldodecyl sulfosuccinate); and hydroxybenzoic acids, suchas glycine-headed-tris(11-acryloyloxyundecyloxy)benzamide andethanolamine-headed-tris(11-acryloyloxyundecyloxy) benzamide, which canbe prepared as described in U.S. Pat. No. 6,884,842 (Soane et al.).

Self-assembly of the monomers to form the surfactant monolayer 24proceeds by surface aggregation of the head groups at the waterinterface with the tail groups organized on hydrophobic surfaces, suchas the hydrophobic trench sidewalls 16 defined in the material layer 12.Polymerization and crosslinking of the monomers can be accomplished byknown reaction methods, including free-radical polymerization, which caninclude the application of radiation, such as UV light, to acceleratethe process. Functional groups such as acrylates can be polymerized byheat or radiation such as UV light. In some embodiments, thepolymerization of the crosslinking groups along the backbone after selfassembly is conducted. Other crosslinking reactions known in the art,such as ring opening, condensation, group transfer, anionic and cationicpolymerization, can optionally be used. Catalysts and/or photo- orthermal-initiators can optionally be used to promote crosslinkingExamples of crosslinking groups include acrylates, methacrylates,acrylamides, vinyl ethers, epoxides, methacrylamides, vinylbenzenes,α-methylvinylbenzenes, divinylbenzenes, vinyl ethers, maleic acidderivatives, fumaric acid derivatives, alkenes, dienes, alkynes,substituted dienes, thiols, alcohols, amines, carboxylic acids,carboxylic anhydrides, carboxylic acid halides, aldehydes, ketones,isocyanates, succinimides, carboxylic acid hydrazides, glycidyl ethers,silanes, siloxanes, chlorosilanes, alkoxysilanes, azides,2′-pyridyldithiols, phenylglyoxals, iodos, maleimides, aryl halides,imidoesters, dibromopropionates, and iodacetyls. In addition tocrosslinking, the surfactant layer can be formed by the condensation ofpolymeric surfactants by changing the solubility of the polymer or thepolarity, pH, or temperature of the solvent.

Referring now to FIG. 10, the aqueous phase polymer component is thencrosslinked to strengthen and form the robust hydrogel 28. Inembodiments using cross-linkable surfactants, a polymer/surfactantemulsion containing such surfactants and the hydrogel-forming precursors(optionally with free radical initiators (either photo- orthermally-activated), hydrogel catalysts, hardening agents, etc.) wouldbe coated onto the substrate 10, and the hydrogel and surfactantcrosslinking can occur about simultaneously or sequentially. In otherembodiments, crosslinking can be achieved by applying a catalyst and/orco-catalyst onto the surface of the aqueous emulsion layer 22, forexample, by spraying or applying drops of a catalyst/co-catalystsolution. For example, in the use of a PEG-based hydrogel materialcomposed of a diacetylene-functionalized PEG derivative, acatalyst/co-catalyst solution of copper sulfate (CuSO₄) and sodiumascorbate can be applied at about room temperature or higher. Furtherhardening can be applied as needed to produce a structure such as therobust hydrogel 28 (FIG. 12A) that is a robust mask for later etching.

Excess material can then be removed, as shown in FIGS. 11 and 11A, toexpose the surfactant monolayer 24 (SAM) along the trench sidewalls 16(and ends 18, referring to the embodiment in FIG. 9B). Removal of theexcess material can be conducted, for example, using a mechanicalplanarization apparatus, such as a grinder. Planarization can also beperformed using a chemical-mechanical planarization (CMP) apparatus withan alkaline slurry containing abrasive particles, for example, analkaline silica or ceria slurry with potassium hydroxide (KOH), sodiumhydroxide (NaOH), tetramethyl ammonium hydroxide (TMAH; (CH₃)₄NOH), andthe like. Removal of the material can also be performed using an etchback process, such as a wet etch process (e.g., using basic conditionsto remove a PEG hydrogel), or a dry etch (e.g., plasma etch) process toetch the hydrogel (and optionally included hardening agent), forexample, a combination of oxygen for the carbonaceous components and afluorocarbon for silica hardening agents (e.g., CH₂F₂, CHF₃, CF₄, etc.).Optionally, the hydrogel can be dried prior to a planarization or etchprocess to reduce the thickness and facilitate the removal process,provided that the structure of the robust hydrogel 28 has enoughstructural integrity to not shift during the drying process.

Referring now to FIGS. 12 and 12A, the surfactant monolayer 24 (FIG.11A) is then selectively removed leaving a void or channel 30 along thetrench sidewalls 16 that is the width of the surfactant monolayer 24(e.g., up to about 10 nm wide) and the crosslinked, robust hydrogel 28intact within the center of the trenches 14. In embodiments in which thesurfactant monolayer 24 is not crosslinked, selective removal of thesurfactant monolayer 24 can be achieved, for example, by a wet etchprocess with an appropriate solvent (e.g., water, alcohols, aromatichydrocarbons, such as toluene and xylene) or by dry etch. In otherembodiments, a crosslinked surfactant monolayer 24 can be removed by aselective dry etch (e.g., plasma etch) process, for example, an oxygenplasma “ashing” process, or other appropriate technique.

The resulting structure is composed of a pair of channels (lines) 30 upto about 10 nm wide (e.g., about 3-10 nm wide) and registered to thetrench sidewalls 16. Each pair of channels 30 within a trench 14 isseparated from each other by the width (w_(h)) of the hydrogel (e.g.,the robust hydrogel 28) within the trench 14, and from a channel 30 inan adjacent trench 14 by the width (w_(s)) of the spacer 12 a betweenthe trenches 14. The hydrogel film (i.e., the robust hydrogel 28) can bethen used, for example, as a lithographic template or mask to pattern(arrows ↓↓) the underlying substrate 10 in a semiconductor processing,for example, by a non-selective RIE etching process, to define a seriesof channel or grooves 32 (shown in phantom lines in FIG. 12A) in thesub-10 nanometer size range. The grooves 32 can then be filled, forexample, with a conductive material (e.g., metal) to form nanowirechannel arrays for transistor channels, semiconductor capacitors, and toform nanowire channel arrays for transistor gates and digit lines. Thegrooves 32 may be filled with a dielectric material to definesource/drain active areas. Further processing can then be performed asdesired.

Another method according to an embodiment of the invention, illustratedwith reference to FIGS. 13-19, utilizes a graphoepitaxy technique thatinvolves the use of a lithographical-defined (first) trench to direct alamellar-phase block copolymer film to self assemble into a lamellararray of alternating perpendicular-oriented polymer-rich blocks thatextend the length and are ordered and registered to the sidewalls of the(first) trench. Selective removal of one of the blocks forms a series ofabout 10-30 nanometer-scale parallel lines that can be used as atemplate or mask to etch about 10-30 nm grooves (second trenches) intothe underlying substrate within the wider first trench. Theabove-described polymer/surfactant emulsion can then be formed withinthe second trenches and processed to form the hydrogel mask to etch aseries of sub-10 nanometer-scale grooves in the underlying materiallayer.

To produce a polymer film within the first trench using a lamellar-phaseblock copolymer, the surfaces of the sidewalls and ends of the trenchare preferential wetting by the one block of the copolymer and thetrench floor is neutral wetting (equal affinity for both blocks of thecopolymer) to allow both blocks of the copolymer material to wet thefloor of the trench. Entropic forces drive the wetting of a neutralwetting surface by both blocks, resulting in the formation of a singlelayer of lamellae across the width of the trench.

In some embodiments, the second trenches are structured with hydrophilicfloors and ends, such that the aqueous phase of the emulsion wets bothof those surfaces, and hydrophobic sidewalls, such that the surfactantlayer forms solely along that surface (as in FIG. 9).

For example, in an embodiment shown in FIGS. 13-13B, a substrate 10″ isprovided bearing a neutral wetting layer 36″ having a neutral wettingsurface. The substrate 10″ can comprise, for example, silicon oramorphous (transparent) carbon or a metal film (e.g., gold, aluminum,etc.). The substrate 10″ overlies a sub-material layer 34″, which, insome embodiments, comprises an oxide (e.g., silicon oxide, SiO_(x)),which is inherently hydrophilic.

As shown, a silicon layer in the substrate 10″ has been etchedlithographically to form trenches 11″ to the underlying sub-SiO_(x)layer (i.e., sub-material layer 34″, and the trenches 11″ filled with aSiO_(x) layer 13″, as described with reference to FIGS. 2-4B.

The neutral wetting surface 36″ is formed on the substrate 10″ prior toforming the overlying material layer 12″. As illustrated in FIGS.14-14B, etching through the material layer 12″ to form a first trench38″ exposes the underlying neutral wetting surface 36″ as the floor orbottom surface 40″ of the trench 38″.

The neutral wetting surface can be provided, for example, by applying aneutral wetting polymer to form a neutral wetting layer 36″ on thesurface of the substrate 10″. In the use of a self-assembling (SA)diblock copolymer composed of PS-b-PMMA, a random PS:PMMA copolymerbrush layer (PS-r-PMMA)) that exhibits non-preferential or neutralwetting toward PS and PMMA can be applied by spin-coating onto thesurface of substrate 10″. The brush can be affixed by grafting (on anoxide substrate or native oxide layer) or by crosslinking (any surface)using UV radiation or thermal processing. For example, a randomcopolymer solution composed of PS and PMMA with hydroxyl end groups(e.g., about 58% PS) can be applied to the surface of the substrate 10″as a layer about 5-10 nm thick and end-grafted by heating at about 160°C. for about 48 hours.

A trench floor that is neutral wetting to PS-b-PMMA can also be preparedby spin coating a photo- or thermally-cross-linkable random copolymer,such as benzocyclobutene- or azidomethylstyrene-functionalized randomcopolymers of styrene and methyl methacrylate (e.g.,poly(styrene-r-benzocyclobutene-r-methyl methacrylate)(P(S-r-BCB-r-MMA))), onto the surface of the substrate 10″ and thermallycrosslinking the polymer (e.g., at about 200° C. for about 4 hours) toform a cross-linked polymer mat as a neutral wetting layer 36″.

Another neutral wetting surface for PS-b-PMMA can be provided byhydrogen-terminated silicon, which can be prepared by a conventionalprocess, for example, by a fluoride ion etch of a silicon substrate 10″(with native oxide present, about 12-15 Å), for example, by immersion inaqueous solution of hydrogen fluoride (HF) and buffered HF or ammoniumfluoride (NH₄F), by HF vapor treatment, by exposure to hot H₂ vapor, orby a hydrogen plasma treatment (e.g., atomic hydrogen).

In another embodiment shown in FIG. 14C, the material layer 12″ can beformed on the substrate 10″ and etched to form the first trench 38″, anda neutral wetting material for the neutral wetting layer 36″ thenapplied to the trench floor 40″. For example, a cross-linkable randomcopolymer can be spin coated onto the surface of the substrate 10″within the first trench 38″ and crosslinked to form a crosslinkedpolymer mat as the neutral wetting layer 36″. Capillary forces pull therandom copolymer to the bottom of the first trench 38″. Non-crosslinkedpolymer material can be subsequently removed. A neutral-wetting polymer(NWP), such as random copolymer of P(S-r-MMA-r-HEMA), can also begrafted selectively to a material layer, e.g., an oxide floor. See, forexample, Insik In et al., Side-Chain-Grafted Random Copolymer Brushes asNeutral Surfaces for Controlling the Orientation of Block CopolymerMicrodomains in Thin Films, 22 LANGMUIR 7855-60 (2006), the disclosureof which is incorporated by reference herein. In other embodiments, anolefinic monomer, such as PMMA or PS, can be grafted onto anH-terminated silicon substrate 10″ (i.e., floor 40″) by an in situ freeradical polymerization using a di-olefinic linker, such as divinylbenzene to produce an about 10-15 nm thick film.

As shown in FIGS. 14-14B, a material layer 12″ is formed on thesubstrate 10″ and patterned to form the first trench 38″ structured witha floor or bottom surface 40″, opposing sidewalls 42″, opposing ends(edges) 44″, a width (w), a length (l) and a depth (D). The first trench38″ can be formed by a lithographic technique, for example,photolithography, extreme ultraviolet (EUV) lithography, proximityX-rays, and electron beam (e-beam) lithography, as known and used in theart.

The trench sidewalls 42″ and ends 44″ are preferential wetting by oneblock of the copolymer to induce formation of lamellar polymer domainsas the blocks self-assemble. The material layer 12″ defining the trenchsurfaces (e.g., sidewalls 42″ and ends 44″) can be an inherentlypreferential wetting material, or in other embodiments, a layer of apreferential wetting material can be applied onto the surfaces of thefirst trench 38″. For example, in the use of poly(styrene-block-methylmethacrylate) (PS-b-PMMA), the material layer 12″ can be composed of anoxide (e.g., silicon oxide, SiO_(x)) or a clean silicon surface (withnative silicon oxide), which exhibits preferential wetting toward thePMMA block to result in the assembly of a thin (e.g., 1/4 pitch)interface layer of PMMA and alternating PMMA and PS lamellae (e.g., 1/2pitch) within the first trench 38″ in the use of a lamellar-phase blockcopolymer material. Other preferential wetting surfaces to PMMA can beprovided, for example, by silicon nitride, silicon oxycarbide,polymethylmethacrylate (PMMA) polymer grafted to a sidewall materialsuch as silicon oxide, and resist materials such as methacrylate-basedresists. For example, a PMMA that is modified with a moiety containingone or more hydroxyl (—OH) groups (e.g., hydroxyethylmethacrylate) canbe applied by spin-coating and then heated (e.g., to about 170° C.) toallow the OH groups to end-graft to the oxide sidewalls 42″ and ends 44″of the first trench 38″. Non-grafted material can be removed from theneutral wetting layer 36″ by rinsing with an appropriate solvent (e.g.,toluene). See, for example, P. Mansky et al., ControllingPolymer-Surface Interactions with Random Copolymer Brushes, 275 (5305)SCIENCE 1458-60 (1997), and Insik In et al., Side-Chain-Grafted RandomCopolymer Brushes as Neutral Surfaces for Controlling the Orientation ofBlock Copolymer Microdomains in Thin Films, 22 LANGMUIR 7855-60 (2006),the disclosures of each of which are incorporated by reference herein.

The trench sidewalls 42″, ends 44″, and floor 40″ influence thestructuring of the array of lamellae within the first trench 38″. Theboundary conditions of the trench sidewalls 42″ in both the x- andy-axis impose a structure such that the first trench 38″ contains nnumber of lamellae. Factors in forming a single array or layer oflamellae within the first trench 38″ include the width and depth of thefirst trench 38″, the formulation of the block copolymer to achieve thedesired pitch (L_(o)), and the thickness (t) (FIG. 15) of the copolymerfilm.

The first trench 38″ is constructed with a width (w) such that alamellar-forming block copolymer (or blend) will self assemble uponannealing into a single layer of “n” lamellae spanning the width (w) ofthe first trench 38″, with each lamellar domain being separated by avalue of L_(o) (from center-to-center). The width (w) of the firsttrench 38″ is a multiple of the inherent pitch value (L_(o)) of theblock copolymer being equal to or about nL_(o) (“n*L_(o)”), typicallyranging from about n*10 to about n*100 nm (with n being the number offeatures or structures). In embodiments of the inventions, the depth (D)of the first trench 38″ is greater than or at about L_(o), asillustrated in FIG. 14A. The application and annealing of a blockcopolymer material having an inherent pitch value of L_(o) in a firsttrench 38″ having a width (w) at or about L_(o) will result in theformation of a single layer of “n” lamellae spanning the width (w) andregistered to the sidewalls 42″ for the length of the first trench 38″.In some embodiments, the dimensions of the first trench 38″ are about55-80 nm wide (w) and about 1600-2400 μm in length (l), with a depth (D)of about 50-500 nm.

Referring now to FIG. 15, a layer 46″ of a lamellar-phaseself-assembling (SA) block copolymer material having an inherent pitchat or about L_(o) (or a ternary blend of block copolymer andhomopolymers blended to have a pitch at or about L_(o)) is thendeposited, typically by spin casting (spin-coating), onto the floor 40″of the first trench 38″. The block copolymer material can be depositedonto the patterned surface by spin casting from a dilute solution (e.g.,about 0.25-2 wt % solution) of the copolymer in an organic solvent, suchas dichloroethane (CH₂Cl₂) or toluene, for example.

The lamellar-phase block copolymer material is deposited into the firsttrench 38″ to a thickness (t) less than the trench depth (D), forexample, at about one-half of the trench depth (D), and at or about theL_(o) value of the block copolymer material such that the copolymer filmlayer will self assemble upon annealing to form a single layer oflamellae across the width (w_(t)) of the first trench 38″. A typicalthickness (t) of the block copolymer film (i.e., layer 46″) is about±20% of the L_(o) value of the polymer (e.g., about 10-100 nm) to formalternating polymer-rich lamellar blocks, each with a width of aboutL_(o) (e.g., 25-35 nm) across the width (w) of the first trench 38″. Thethickness (t) of the layer 46″ can be measured, for example, byellipsometry techniques. As shown, a thin film of less than L_(o) of theblock copolymer material can be deposited onto the surface of thematerial layer 12″; this thin film will not self-assemble as it is notthick enough to form structures.

The volume fractions of the two blocks (AB) of the lamellar-formingdiblock copolymer are generally at a ratio between about 50:50 and60:40. An example of a lamellae-forming symmetric diblock copolymer ispoly(styrene-block-methyl methacrylate) (PS-b-PMMA), with a weight ratioof about 50:50 (PS:PMMA) and total molecular weight (M_(n)) of about 51kg/mol.

Although diblock copolymers are used in the illustrative embodiments,other types of block copolymers (i.e., triblock or multiblockcopolymers) can be used. Examples of diblock copolymers includepoly(styrene-block-methyl methacrylate) (PS-b-PMMA),polyethyleneoxide-polyisoprene, polyethyleneoxide-polybutadiene,polyethyleneoxide-polystyrene, polyethyleneoxide-polymethylmethacrylate,polystyrene-polyvinylpyridine, polystyrene-polyisoprene (PS-b-PI),polystyrene-polybutadiene, polybutadiene-polyvinylpyridine, andpolyisoprene-polymethylmethacrylate, among others. Examples of triblockcopolymers include poly(styrene-block methyl methacrylate-block-ethyleneoxide). One of the polymer blocks of the block copolymer should beselectively and readily removable in order to fabricate an etch mask ortemplate from the annealed film.

The block copolymer material can also be formulated as a binary orternary blend comprising a SA block copolymer and one or morehomopolymers of the same type of polymers as the polymer blocks in theblock copolymer, to produce blends that swell the size of the polymerdomains and increase the L_(o) value of the polymer. The volume fractionof the homopolymers can range from 0% to about 40%. An example of aternary diblock copolymer blend is a PS-b-PMMA/PS/PMMA blend, forexample, 46K/21K PS-b-PMMA containing 40% 20K polystyrene and 20Kpoly(methylmethacrylate). The L_(o) value of the polymer can also bemodified by adjusting the molecular weight of the block copolymer, e.g.,for lamellae, L_(o)˜(MW)^(2/3).

Referring now to FIGS. 16-16B, the block copolymer film (i.e., layer46″) is then annealed to form a self-assembled lamellar film 48″, forexample, by thermal annealing to above the glass transition temperatureof the component blocks of the copolymer material to cause the polymerblocks to separate and self assemble into blocks 50″, 52″ according tothe preferential and neutral wetting of the trench surfaces, i.e.,floors 40″, sidewalls 42″, and ends 44″. A PS-b-PMMA copolymer film canbe annealed, for example, at about 180-195° C. in a vacuum oven forabout 1-170 hours to produce a self-assembled film. The self-assembledlamellar film 48″ can also be solvent annealed, for example, by slowlyswelling both blocks 50″, 52″ of the self-assembled lamellar film 48″with a solvent, then slowly evaporating the solvent.

The constraints provided by the width (w) of the first trench 38″ andthe character of the block copolymer composition combined withpreferential and neutral wetting surfaces within the first trench 38″results, upon annealing, in a single layer of n perpendicular-oriented,alternating lamellar polymer-rich blocks extending the length (l) andspanning the width (w) of the first trench 38″ at an average pitch valueof at or about L_(o) (center-to-center). The number “n” or pitches oflamellar blocks within the first trench 38″ is according to the width(w) of the first trench 38″ and the molecular weight (MW) of thecopolymer. For example, depositing and annealing an about 50:50 PS:PMMAblock copolymer film (M_(n)=51 kg/mol; L_(o)=32 nm) in an about 250 nmwide first trench 38″ will subdivide the first trench 38″ into abouteight (8) lamellar structures. The perpendicular orientation of lamellaecan be examined, for example, using atomic force microscopy (AFM),transmission electron microscopy (TEM), or scanning electron microscopy(SEM).

The annealed and ordered film (i.e., the self-assembled lamellar film48″) can then be treated to crosslink the polymer segments to fix andenhance the strength of the self-assembled polymer blocks 50″, 52″within the first trench 38″ (e.g., to crosslink the PS segments). Thepolymers can be structured to inherently crosslink (e.g., upon UVexposure through a reticle), or one or both of the polymer blocks 50″,52″ of the copolymer material can be formulated to contain acrosslinking agent. The substrate 10″ can then be washed with anappropriate solvent, such as toluene, to remove the non-crosslinkedportions of the self-assembled lamellar film 48″ on surfaces outside thefirst trench 38″ (e.g., on the crest 12 a″) leaving the registered,self-assembled lamellar film 48″ within the first trench 38″ (FIG. 16A).

Referring now to FIGS. 17-17B, after the lamellar-phase block copolymermaterial is annealed and ordered to form the self-assembled lamellarfilm 48″, one of the block components (e.g., block 50″) can beselectively removed to produce a thin film 54″ having registered andparallel oriented openings (slits) 56″ that can be used, for example, asa lithographic template or mask to pattern the underlying substrate 10″within the first trench 38″ in a semiconductor processing to defineregular patterns in the nanometer size range (i.e., about 10-100 nm).For example, selective removal of one of the block components, block 50″(e.g., the PMMA domains) will result in openings (slits) 56″ separatedby another of the block components, block 52″ (e.g., vertically orientedPS lamellar domains) with the trench floor 40″ (e.g., neutral wettinglayer 36″ over substrate 10″) exposed where the first blocks 50″ (i.e.,the PMMA blocks) were removed. Removal of the first blocks 50″ (e.g.,the PMMA phase domains) can be performed, for example, by application ofan oxygen (O₂) plasma or CF₄ plasma (e.g., about 3:1 selective forPMMA), or by a chemical dissolution process such as acetic acidsonication by first irradiating the sample (ultraviolet (UV) radiation,1 J/cm² 254 nm light), then ultrasonicating the self-assembled lamellarfilm 48″ in glacial acetic acid, ultrasonicating in deionized water, andrinsing the self-assembled lamellar film 48″ in deionized water toremove the degraded PMMA (i.e., the first blocks 50″).

In some embodiments, the resulting thin film 54″ will have a corrugatedsurface that defines a linear pattern of fine, nanometer-scale parallelopenings (slits) 56″ about 10-60 nm wide and extending the length of thefirst trench 38″, the individual openings (slits) 56″ separated by apolymer matrix of the second blocks 52″ (e.g., of PS) about 10-60 nmwide. For example, removal of the PMMA domains (i.e., first blocks 50″)(from PS-b-PMMA of MW 51K) affords a PS (i.e., second block 52″) mask ofsub-lithographic dimensions, for example, a pitch of about 32 nm (16 nmPS domain). A smaller pitch can be dialed in by using lower molecularweight diblock copolymers.

The thin film 54″ can then be used as a lithographic template or etchmask to pattern (arrows ↓↓) the underlying substrate 10″ (e.g.,silicon), for example, by a non-selective RIE etching process, todelineate a series of trenches (grooves, channels) 14″ as illustrated inFIGS. 18A and 18B. The residual thin film 54″ (e.g., polystyrene) canthen be removed, for example, by an etch using a low density plasma ofoxygen, resulting in the structure shown in FIG. 19.

Etching through the substrate 10″ (e.g., silicon) to form the trenches14″ exposes the underlying sub-material layer 34″, which is oxide in theillustrated example, as the floor or bottom surface 20″ of the trenches14″, the oxide layer (i.e., SiO_(x) layer 13″) as the ends 18″, andsubstrate 10″/10 a″, which is silicon in the illustrated example, as thesidewalls 16″. In some embodiments, the dimensions of the trenches 14″are about 10-60 nm wide (w_(t)) and about 10-100 nm deep with a depth(D_(t)).

As previously described with reference to FIGS. 5-5B, an aqueousfluoride treatment can be briefly conducted to remove native oxide onthe silicon layer of the substrate 10″ (to form H-terminated siliconsidewalls 16″) while minimizing etching of the SiO_(x) layer 13″ andsub-material layer 34″. A PEG coupling agent can then be applied aspreviously described, for example, by grafting a ligand with a reactiveend group such as a mono-hydroxylated PEG ligand to hydroxyl (—OH)groups on the SiO_(x) floor 20″ and ends 18″ of the trenches 14″ in aninert atmosphere (e.g., nitrogen, argon, etc.) to minimize thereformation of native oxide on the silicon sidewalls 16″.

As described with reference to FIGS. 9-12A, the previously describedaqueous polymer/surfactant emulsion can then be applied to fill thetrenches 14″ and processed to form an etch mask composed of the hydrogelmaterial to etch the sub-material layer 34″ to form grooves or channels(e.g., 32 shown in phantom lines in FIG. 12A).

Another method according to an embodiment of the invention isillustrated with reference to FIGS. 20-24. In some embodiments, asubstrate 10″′, such as the substrate 10 as described with respect toFIGS. 5-5B (or the substrate 10′ as described with respect to FIGS. 8and 8A) can be prepared having trenches 14″′ with a hydrophilic floor20″′, hydrophilic ends 18″′ (e.g., of SiO_(x)), and hydrophobicsidewalls 16″′ (e.g., H-terminated silicon).

Referring now to FIG. 20, an aqueous emulsion (for an aqueous emulsionlayer 58″′) composed of a self-assembling amphiphilic agent, e.g.,surfactant monomers, for example, as described above with reference toU.S. Pat. No. 6,884,842 (Sloane et al.), containing olefinic group(s)with surface functional head groups that are complementary to asubstrate surface, can be applied to fill the trenches 14″′ and over thematerial layer 12″′. The emulsion can be applied, for example, bycasting, dip coating, spray coating, knife-edge coating, spin casting(spin-coating), and the like, such that the emulsion layer 58″′ ismaintained in a liquid consistency to allow a layer of the amphiphilicagent (e.g., surfactant) to form at the trench hydrophobic sidewalls16″′. Application of the emulsion can be conducted at about roomtemperature (e.g., about 20-25° C.) to up to about 95° C. Theamphiphilic agent (e.g., surfactant monomers) will self-assemble to forma surfactant monolayer 24″′ on the hydrophobic sidewalls 16″′ (e.g.,H-terminated silicon) of the trenches 14″′. The monomers can then bepolymerized and crosslinked, for example, by free-radicalpolymerization, to form a robust, thin, insoluble surfactant monolayerfrom the surfactant monolayer 24″′.

As shown in FIG. 21, the robust surfactant monolayer 24″′ can then bedried, for example, by heating and/or blow-drying with a dry gas such asnitrogen, argon, and clean dry air, or by a Marangoni drying techniquein which the structure is immersed in a DI water bath and drawn througha layer of a water-miscible solvent that is more volatile than watersuch as isopropyl alcohol (IPA), which rests on the surface of the DIwater bath. Micellar structures or other material that has precipitatedonto the trench hydrophilic floor 20″′ and hydrophobic sidewalls 16″′during crosslinking of the surfactant monomers can be removed, forexample, by rinsing or sonicating using a liquid that does not swell thecrosslinked surfactant material or cause dewetting of the surfactantmonolayer, for example, water, methanol, and isopropanol.

Referring now to FIG. 22, an inorganic material layer 60″′ such as adielectric material can then be deposited, for example, by a chemicaldeposition process at a low temperature such that the robust surfactantmonolayer 24″′ is not degraded (e.g., below about 150° C.), to fill thetrenches 14″′. Suitable dielectric materials include, for example,silicon oxide (SiO_(x)), aluminum oxide (Al₂O₃), tantalum oxide(TaO_(x)), silicon carbide (SiC), hafnium oxide (HfO₂), hafnium aluminumoxide (HfAlO), silicon carbon nitride (SiCN), silicon nitride (SiN₄),yttrium oxide (YO₂), and tantalum pentoxide (Ta₂O₅). Excess material canthen be removed as in FIG. 23, for example, by mechanical planarization,chemical-mechanical planarization, or an etch back process, to exposethe robust surfactant monolayer 24″′ along the trench hydrophobicsidewalls 16″′.

As depicted in FIG. 24, the surfactant monolayer 24″′ along the trenchhydrophobic sidewalls 16″′ can then be selectively removed, leaving achannel or gap 30″′ that is the width of the surfactant monolayer 24″′(e.g., up to about 10 nm wide), with the inorganic material layer 60″′remaining intact within the center of the trenches 14″′. Selectiveremoval of the crosslinked (i.e., robust) surfactant monolayer 24″′ canbe achieved, for example, by a selective dry etch (e.g., plasma etch)process, for example, an oxygen plasma “ashing” process, or otherappropriate technique.

The resulting structure is composed of a pair of channels (lines) orgaps 30″′ up to about 10 nm wide (e.g., about 3-10 nm wide) andregistered to the trench hydrophobic sidewalls 16″′. Each pair ofchannels or gaps 30″′ within a trench 14″′ is separated from each otherby the width (w_(x)) of the inorganic material layer 60″′ within thetrench 14″, and from a channel or gap 30″′ in an adjacent trench 14″′ bythe width (w_(s)) of the spacer 12 a″′ between the trenches 14″′. Theinorganic material layer 60″′ can be then used, for example, as alithographic template or mask to pattern (arrows ↓↓) the underlyingsubstrate 10″′, for example, by a non-selective RIE etching process, todefine a series of channels or grooves 32″′ (shown in phantom lines inFIG. 24) in the sub-10 nanometer size range, which can be filled withmetal or other conductive material, or dielectric material, for example.

The described films are useful as lithographic templates or etch masksfor producing close-pitched, ordered, and registered, nanoscale channelsand grooves that are sub-10 nm wide and several nanometers in length,for producing features such as floating gates for NAND flash withnanoscale dimensions. By comparison, photolithography techniques areunable to produce channels much below 60 nm wide without high expense.Resolution can exceed other techniques for forming channels and grooves,including self-assembling block copolymer processing and conventionalphotolithography. Fabrication costs utilizing methods of the disclosureare far less than electron beam (e-beam) or EUV photolithographies,which have comparable resolution.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement that is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. This application isintended to cover any adaptations or variations that operate accordingto the principles of the invention as described. Therefore, it isintended that this invention be limited only by the claims and theequivalents thereof. The disclosures of patents, references andpublications cited in the application are incorporated by referenceherein.

1. A method for forming a polymeric material, comprising: depositing anaqueous emulsion comprising an amphiphilic material in a trench havinghydrophobic sidewalls and a hydrophilic floor, wherein the amphiphilicmaterial selectively assembles on the sidewalls of the trench;crosslinking the amphiphilic material; and drying the amphiphilicmaterial.
 2. The method of claim 1, further comprising, after drying theamphiphilic material layer, filling the trench with an inorganicmaterial.
 3. The method of claim 2, further comprising, after depositingthe aqueous emulsion in the trench, removing a portion of the inorganicmaterial and amphiphilic material above the trench to expose theamphiphilic material on the sidewalls of the trench.
 4. A structure fora template for etching a substrate, comprising an inorganic materialwithin a trench in a material overlying the substrate and a crosslinkedamphiphilic material on sidewalls of the trench.
 5. A template structureetching a substrate, comprising: a trench having a floor, ends, andnon-hydrophilic sidewalls; a cross-linked amphiphilic material on thenon-hydrophilic sidewalls of the trench, the cross-linked amphiphilicmaterial having a thickness of up to about 10 nm; and an inorganicmaterial filling the trench.
 6. The template structure of claim 5,wherein the floors and the ends are hydrophilic.
 7. The templatestructure of claim 5, wherein: the substrate comprises silicon oxide;and the floor of the trench is defined at a surface of the substrate. 8.The template structure of claim 5, wherein the cross-linked amphiphilicmaterial defines at least one elongated monolayer along thenon-hydrophilic sidewalls of the trench.
 9. The method of claim 1,wherein depositing an aqueous emulsion comprises depositing an aqueousemulsion comprising the amphiphilic material comprising olefinic groups.10. The method of claim 1, wherein drying the amphiphilic materialcomprises at least one of heating and blow-drying with a dry gasselected from the group consisting of nitrogen, argon, and air.
 11. Themethod of claim 1, wherein drying the amphiphilic material comprises:immersing the amphiphilic material in a deionized water bath; anddrawing the amphiphilic material through a water-miscible solvent. 12.The method of claim 1, further comprising filling the trench with adielectric material.
 13. The method of claim 12, wherein filling thetrench with a dielectric material comprises filling the trench with atleast one of silicon oxide (SiO_(x)), aluminum oxide (Al₂O₃), tantalumoxide (TaO_(x)), silicon carbide (SiC), hafnium oxide (HfO₂), hafniumaluminum oxide (HfAlO), silicon carbon nitride (SiCN), silicon nitride(SiN₄), yttrium oxide (YO₂), and tantalum pentoxide (Ta₂O₅).
 14. Themethod of claim 1, further comprising, before depositing the aqueousemulsion: forming other trenches in a material on a substrate; fillingthe other trenches with silicon oxide; and forming the trench in thematerial, the trench extending between the other trenches and exposingthe silicon oxide along ends of the trench.
 15. The method of claim 1,further comprising, before depositing the aqueous emulsion formingsilicon oxide along ends of the trench.
 16. The method of claim 2,further comprising, after filling the trench with the inorganicmaterial, removing the amphiphilic material.
 17. The method of claim 16,further comprising, after removing the amphiphilic material, patterningthrough gaps defined by removing the amphiphilic material and into asubstrate supporting the inorganic material.
 18. The structure of claim4, wherein the material overlying the substrate comprises siliconoverlying the substrate.
 19. The structure of claim 4, wherein thesidewalls of the trench are hydrophobic.
 20. The structure of claim 4,wherein the inorganic material directly contacts floors of the trench.